Configuration of closed kinematic chains in SDF

Is there a tutorial or documentation on how to setup closed kinematic chains?
I have found some material on the internet (like this one https://www.youtube.com/watch?v=Vpfxjh4mPXk&feature=youtu.be) but I had a hard time implementing it on my model.
Any material available?

Technical help questions, such as this, should be asked on answers.gazebosim.org. This forum is designed for general discussions, community organization, news, and other topics.

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There is an answer on answers.gazebosim.org that should help you(http://answers.gazebosim.org/question/7308/parallel-robots-implementing-close-kinematic-chains/).